New Terms

Frame

An armor’s frame describes its core component and, most relevantly, how mobile a user is while wearing it. While frame often corresponds to the three tiers of armor (light, medium, heavy), there are clearly just as many counterexamples.

Jack: This armor is flexible and easy to move in. Most are made of canvas or leather, often reinforced in places. While you wear light armor, you add your Dexterity modifier to your Armor Class.

Hauberk: A hauberk is a shirt of armor that is flexible enough to still dodge blows, but is restricts the wearer’s agility more than a jack. The most common hauberk is made of interlocking links of steel or iron chain. When you wear a hauberk, add the lower of your Dexterity or Strength modifier to your Armor Class, rather than your Dexterity modifier. In other words, your Dexterity does modify your AC, but only to the extent allowed by your Strength. No matter how quick you are, if your Strength score is only 10 then this armor is too heavy for you to get the most out of. This is mathematically equal to “your max Dex bonus is equal to your Strength modifier,” but it achieves simplicity at perhaps the cost of obviousness.

Cuirass: The most formidable armor is built around a rigid carapace protecting the wearer’s vital organs. This chestplate is augmented with additional protection over the wearer’s extremities. When you wear a cuirass, you do not add your Dexterity bonus to your Armor Class. However, you still deduct your Dexterity penalty, if your Dexterity is less than 10.

Qualities

Concealed: This armor consists of protective reinforcement sewn into otherwise ordinary looking clothing. It appears as if the wearer is not unarmored unless an observer succeeds on a DC 15 Wisdom (Spot) check. If the observer is physically handling the armor, this check is made with advantage.

Noisy: This type of armor reduces your ability to move quietly. Generally, the cause of this noise is metal components of the armor striking against each other. When you wear noisy armor, any ability checks that you make to move silently (this is most often a Dexterity (Stealth) check) are made with disadvantage. Other situations—hiding without moving at all, moving while magically silenced—are up to the DM.

Encumbrance

Encumbrance is an alternative to tracking carrying capacity according to weight. It has two advantages. First, it conveys both the weight and bulkiness of the armor. Secondly, it represents a much more strategic factor in outfitting a character than weight alone, since encumbrance is generally a more limited resource. This second advantage is the most important in terms of the design of this rules module, as it facilitates another point of balance between different armor types.

Armored Coat: This long coat is reinforced with stiffened layers of leather. It protects the wearer’s most vital organs from indirect blows and is mostly undetectable from a cursory glance.

Worn by: duelists, fencers, pirates

It’s lighter protection than even other forms of light armor, but note that it has a special quality allowing you to conceal the fact that you’re wearing armor. It’s like you’re wearing nothing at all! (Nothing at all!)

Leather: Leather armor is sturdy but light. It protects vital areas with multiple layers of boiled-leather plates, while covering the limbs with supple leather that provides a small amount of protection.

Worn by: Thieves, assassins.

Leather armor is the way to go if you want full Dexterity bonuses, with no loss of stealth. As such, it's really just the minimal protection worn by extremely elusive characters.

Chain Shirt: A light set of chain links with a leather cap, this armor provides full mobility, as well as the protection of metal armor.

Worn by: Bards, Strength rogues

Chain shirts are the choice of adventurers who want the best AC that light armor can afford. For most light armor wearers, the stealth disadvantage isn't worth the small bit of extra protection, but you might see a bard wearing it.

Hide Armor: Hide armor is made from the tanned skin of particularly thick-hided beasts, stitched with either multiple overlapping layers of crude leather or exterior pieces of leather stuffed with padding or fur. Damage to the armor is typically repaired by restitching gashes or adding new pieces of hide, giving the most heavily used suits a distinctively patchwork quality.

Worn by: Barbarians, druids.

You might like hide armor if you have a moderate score in both Strength and Dexterity. The difference between rangers that wear studded leather armor and rangers that wear hide comes down to this Str/Dex tradeoff.

Studded Leather: Studded leather is leather armor reinforced with metal studs. It provides increased protection, with only a small impact on the wearer's mobility.

Worn by: Skirmishing fighters, fighter/rogues, archers.

If you have a high Dexterity, consider whether studded leather is worth investing in medium armor proficiency. Studded leather is a staple of D&D, and remains an attractive option here.

Chainmail: Metal rings woven together into a shirt, leggings, and a hood make up a suit of chainmail. Chainmail grants good protection, but it’s cumbersome, so it reduces your mobility and agility.

Worn by: Clerics, warlords

Chainmail is practically heavy armor. It has the weight and reduced stealth of heavier armors, but a slightly higher AC than the other mediums, if heavy proficiency isn't worth buying to you.

Breastplate: A breastplate covers the front and back of the chest. It comes with a helmet and matching greaves, and often also a leather fauld. It is sturdier protection than non-metal armor, but less flexible than other medium options.

Worn by: Gladiators, guardsmen.

Go for it. If you want an AC similar to heavy armor but you have nothing to lose in the Dexterity department, then it’s probably a good deal.

Scale Mail: Overlapping pieces of steel make up scale armor. Despite its heaviness, scale is surprisingly easy to wear; its straps and buckles make it adjustable and able to fit snugly on the body, allowing for flexibility and agility. Scale mail is a common sight on mercenaries and soldiers.

Worn by: Mercenaries, soldiers.

If you have heavy armor proficiency, but still have a decent Dexterity, take scale mail. The end result is an awesome AC.

Splint Mail: This armor is made from metal banding attached to a semi-rigid backing. It often serves as field plate for knights who need heavy armor for travel, as it does not slow down a trained wearer as much as full plate.

Worn by: Samurai, myrmidons, elven champions.

This is a nice choice for fighters who want to still be somewhat light on their feet.

Brigandine: Brigandine armor is made of steel plates riveted to a backing of leather and chain.

Worn by: Knights in the field, legionnaires, generals on campaign.

If you want generally reliable armor without investing in Dexterity, but that last point of AC isn’t worth the extra encumbrance and Stealth disadvantage, then you might be tempted away from plate mail.

Plate Mail: The heaviest type of armor, made up of shaped plates of steel or similarly resilient material, plate provides the most armor protection. The cost for its superior fortification is mobility and agility.

Worn by: Paladins, baby! Also, antipaladins.

You don't care about Dexterity, encumbrance, or stealth? You're a madman! But okay, you can have the highest AC on the table.